This proposal deals with the sarcoplasmic reticulum (SR) and surface membranes (plasmalemma and T-system) of heart and skeletal muscle. A vital role of these two membrane systems is the release and uptake of Ca2 ions, which induces contraction and relaxation in muscle. Our long-term goal is to characterize these membranes both structurally and functionally in molecular terms. We have succeeded in purifying and characterizing distinct types of SR vesicles from skeletal muscle and in reconstituting a functional SR compartment from its solubilized components. We now propose to study the ion permeability and Ca2 ion transport properties of purified SR - T-system junctions (triads), plasmalemma and T-system membranes. We will determine which portion of sarcoplasmic reticulum releases Ca2 ion and the mechanism by which Ca2 ions are released. We will also attempt to identify the Ca2 ions transport systems in plasmalemma and T-system membranes, and establish the function of surface membrane Mg2 ions or Ca2 ions activated ATPase ("basic" ATPase). In addition, we will extend our studies on the in vitro assembly of SR by including components which render the member permeable to K ions, Na ions, and Cl-, and make possible the rapid release of Ca2 ions from SR. We will develop techniques for making vesicles which, like native SR, have an asymmetric protein arrangement within the membrane. The work with normal skeletal muscle will be extended to the isolation and characterization or SR and surface membranes of heart and dystrophic muscle. With a comprehensive examination of SR and T-system function and assembly we should gain insight into the process of excitation-contraction coupling of muscle. This in turn should lead to a better understanding of the action of SR and T-system in the overall function of normal skeletal and heart muscle as well as diseased muscle.